In high current applications, circuit breakers are typically quite large, which makes it difficult to move the circuit breaker to electrically connect and disconnect it from a switchboard without mechanical assistance. Not only does the weight and bulk of the circuit breaker become difficult for the electrician to handle, but, as the current ratings increase, the contact pressures of the primary disconnect contacts become extremely difficult, if not impossible to overcome. To overcome these problems, so-called “draw-out” assemblies are used to support the circuit breaker and provide mechanical assistance to overcome the contact pressures of the disconnect contacts.
Draw-out apparatus are generally designed to support the electrical device for racking movement between an extended position and an engaged position where the load current carrying primary disconnects of the device are fully engaged. As is well known in the art, three-phase draw-out circuit breakers include six primary disconnect bushings that extend rearwardly from the back panel of the circuit breaker. In the past, the back panel was formed by cutting six holes in a stainless steel sheet, then installing individual molded bushings in each hole. Each bushing was bolted in place, and when installed onto the switchgear, an additional formed steel strap was bolted horizontally across the center of the back panel for further support. Though the previous back panel/bushing design is functional, drawbacks persist.
There is therefore a need in the art for improved switchgear rear panel and bushing arrangements.